Process of recovering salts from minerals



:March 3, 1931. E. P. scHoH 1,794,552

PROCESS vOF RECOVERING SALTS FROM MINERALS Filed Dec. 29. 1928 6.3/61. /fzsa 207 fs. )refer EUR Schoch Izzven :for

Patented Mu?. 3, 1931 UNI-TED STATES .PATENT OFFICE EUGENE r. seizoen, or Ausrn, rms

Application tiled December 29, 1928. Serial No. 329,316.

My invention relates to the extraction of salts from minerals and more particularly has reference to a process of obtaining gypsum, potassium sulphate, and magnesium sulphate in substantially pure form from minerals containing the same.

In my prior application Serial No. 300,959, filed August 20, 1928, I have described and claimed a process of obtaining potassium and magnesium sulphates from polyhalite, krugite, and other ores containing the same, which process consists essentially in first heating the ore to a temperature suiiicient to dehydrate the same and then leaching with hot Water to dissolve the soluble potassium and magnesium sulphates. t

It is an object of my present invention to obtain gypsum, potassium sulphate, and magnesium sulphate, each in substantially pure form, from ores containing the same, the process being carried out in an efficient, practical, and economical. manner.

Other objects and advantages will appear from the detailed description of the process,

it being understood, however, that various chan es and modifications may be made therein without departing from the spirit or scope of the invention as" defined in the appended claims.

The process of my present invention is applicable to the treatment generally of minerals or ores containing gypsum, potassium sulphate, and ma esium sulphate. 'Polyhalite (2CaSO.,-K2 O4-MgSOg-2H2O), found in west Texas and New Mexico in fairly pure form, is a common t pe of ore containing gypsum, potassium su phate and magnesium sulphate, and I shall therefore describe my process with reference to the treatment of that mineral. However, it is to be ex ressly understood that my invention is not imited to the treatment of polyhalite as the process may be applied to other ores containing gypsum, potassium sulphate, and magnesium sulphate, for example, krugite.

and others.

ore having been crushed, admixtures of comi mon salt contained therein may first be removed by leaching with cold4v water. The ore will now be found to contain practically only the normal ingredients of polyhalite in the molecular proportions as expressed by the formula,

with the possible exception of a slight excess of calcium sulphate over the amount called for by the formula. l -Y The ore is now calcined orroasted to expel the water of crystallization as in my prior application above referred to and the resulting mass, while still hot, is dropped into water in a leacher, the water being preferably prewarmed suiiiciently to be brou ht to the boiling point by the heat of the ca cined ore. As explained in my prior application, the removal of water of crystallization from the ore enables the potassium and magnesium sulphates to be practically entirely removed in a short time by leaching with hot Water. The amount of water into which the heated ore is introduced may be such as to immediately form a saturated solution with the potassium and magnesium sulphates extracted, but a larger volume of water is preferably employed since further quantities of potassium and magnesium sulphates are added to the extract at subsequent stages in the process as will be hereinafter described. The liquor is now separated from the solid residue in a known manner whicli residue, after removal of excess water, represents the gypsum content of the polyhalite in substantially pure form and is the fir final product of the process.

To the liquor while still at elevated temperature (approximately 212 F.) there'is now added a quantity of potassium and magnesium sulphates obtained in a subsequent stage in the process to be described and the mixture stirred. The added potassium and magnesium sulphates, preferably schoenite produce in the liquor a v'strong solution of potassium sulphate and magnesium sulphate 100 A or the process.

water by evaporation.

To the resulting liquor, that is, the liquor from which the potassium sulphate has been crystallized and removed, there is now added a second quantity of potassium and magnesium sulphates also obtained in a. subseuent stage of the process to be described. he mixture is then cooled to ordinary temperatures by spraying in the air and this spraying or evaporation by aeration at ordinary temperaturas continued until the mixture has lost a substantial part of its During this operation, there separates the first crop of mixed crystals of potassium and magnesium sul` phates or the schoenite crystals which are added to the liquor above mentioned which is about to undergo crystallization for potassium sulphate as already described. In other words, the mixed crystals of potassium and magnesium sulphates separated during the aeration process constitute the first of the two sulphate additions above described, the first addition being the one just prior to potassium sulphate separation.

The liquor is now drained from the crystals of potassium and magnesium sulphates and heated and evaporated hot to remove a further quantity of Water. evaporation there separates a second mixed crystal crop of potassium and magnesium sulphates, this crop constituting the quantity of potassium and magnesium sulphates added to the liquor after the step ofl removing the pure potassium sulphate crystals and prior to the aeration step as above described.

n other Words, the potassium and magnesiurnsulphates separated at this point in the process are returned to the liquor as the above second mentioned addition of potas sium and magnesium sulphates. This second crop of mixed sulphate crystals contains a higher proportion of magnesium sulphate than potassium sulphate, whereas the first crop of mixed sulphate crystals contains a hig er proportion of potassium sulphate.

The liquor is now drained from the crystals and cooled to ordinary temperatures as a result of which cooling there crystallizes a crop of nearly pure magnesium sulphate crystals, the third final product of the process, which is then separated from the remaining liquor. This remaining liquor still contains quantities of potassium and magnesium sulphates and, if desired, may therefore be returned to the last evaporation stage, that is, the stage from which is obtained the second crop of mixed crystals of potassium and magnesium sulphates.

During this i In order to more clearly present my invention, I will now describe a practical embodiment of the process, setting forth specific quantities of materials, temperatures, and other operating conditions. It will be under-v stood, however, that the invention is in no Way limited thereto as variations may become necessary or desirable with varying compositions of the ore treated or with the varying of other factors in the prcoess.

1000 pounds of polyhalite, suitably crushed in any known manner and, if desired, leached with cold Water to` remove common salt, is calcined or roasted at approximately 1000 F. to expel Water of crystallization (about 50 pounds) and then, while still hot, dropped into 1904 pounds of water vpre-warmed to 120 F. There results from this leaching a solid residue of gypsum containing 453. pounds CaSO4 and 120 pounds water, the

se arated liquor containing 198 poundsV gSU4, 289 pounds K250i, and 1784 pounds Water.

To the hot liquor there is now added the first quantity of mixed sulphate crystals 0btained later in the process, this crystal crop comprising 362 pounds MgSO4, 522 pounds KZSO4, and 324 pounds Water. The mixture is stirred at about 212o F. and crystallization allowed to take lace whereupon is separated a crystal crop o? 281 pounds KgSO4 containing about 54% KZC). This crystal crop is removed from the liquor, the latter com risin 560 pounds MgSO4, 530 pounds KZS 4, an 2108 pounds Water.

To the last mentioned liquor there is now added the second quantity of mixed potassium sulphate and magnesium sulphate crystals obtained later in the process, this quantity comprising 76 pounds MgSO4, 50 pounds K2SO4, and 36 pounds of water.

The resulting mixture is now cooled and evaporated at 77 F. by sprayin or by aeration until the liquor has lost a out 970 pounds Water by evaporation and during this operation there is separated the first mixed crop of potassium sulphate and magnesium sulphate crystals which is returned to the system as above explained.

Upon separation of the mixed crystal crop, the liquor is found to contain 274 pounds MgSOil, 561/2 pounds K2SO4, and 850 pounds water. To this is added the liquor obtained farther on-from which a crop of magnesium sulphate crystals has ust been obtained-and which liquor is composed of 283 pounds MgSO4, 39.7 pounds K2SO4, and 848 pounds H2O. The combined liquor contains 557 pounds MgSO4, 96.2 pounds K2SO and 1G93 pounds H2O` and this is next heated and evaporated hot, that is, at about 220o F., to remove about 607 pounds water and during 'this step there is separated the second crystal crop of mixed potassium and magnesium sulphates which 1s returned to the process as exdrained from the mixed crystal crop and .com-` prises 481 pounds..MgSO" 461/2 .pounds K250i, and 1055 pounds Water. This liquor is now cooled to 77 F. and as a result of the cooling there is obtained substantially pure crystals of Epsom salts containing 198 pounds q MgSO4, 7 pounds K2SO4, and 207 pounds Water. Upon separation of the substantially pure magnesium sulphate crystals from the liquor, the latter is found to comprise 283 pounds MgSOr, 40 pounds K2SO4, and 848 pounds water. This liquor is returned to the last evaporation stage, that is, the one at about 220 F., to be further evaporated together with the other liquor .putin as stated. From the foregoing it will be seen that I have devised a practical and economical method of obtaining gypsum, potassium sulphate, and magnesium sulphate in substantially pure form from polyhalite and other minerals containing these salts. The accompanying drawing is a dia rammatic sketch readily showing the steps o this process.

Having described my invention, I claim: 1. The process of recovering gypsum, potassiumsulphate, and magnesium sulphate from ores containing the same which comprises Washing the ore with cold water to remove common salt; heating the ore sufficiently lto expel Water of crystallization leaching the ore while still hot With Warm Water to dis-v solve the potassium and magnesium sulphates; removing the undissolvedug'ypsum from the resultant liquor; mixing lwith the liquor a quantity of potassium and ma ne- .sium sulphates obtained in a later stage o the process; permitting crystallization of potassium sulphate from the resultant mixtureand y removing the same from the system; mixing with the resultant liquor a second quantity of potassium and magnesium sulphates 0btained in a later stage of the'process; aerating the resultant mixture to evaporate Water and to cause crystallization of mixed crystals of potassium and magnesium sulphates; separating the resultant mixture of potassium and magnesium sulphates and utilizing the same as the first mentioned quantity of potassium and magnesium sulphates added to the liquor as above stated; heating the resultant liquor and evaporating the same While hot to remove additional Water and to cause crystallization of a second mixture of potassium and magnesium sulphates; separating said secondl mixture and utilizing the same as the second mentioned quantity of potassium" and magiesium sulphates added to the liquor as above stated; cooling the remaining liquor to thereb v cause crystallization of magnesium sulphate and removing the same from the system; and returning the remaining liquor to the last mentioned'evaporation stage.

2. The process ot recovering gypsum, potassium sulphate, and magnesium sulphate from ores containingl the same which comprises heating theore 'suiciently to expel Water of crystallization; leaching the ore while still hot with water to dissolve the potassium and magnesium sulphates; removing the undissolved ypsum from the resultant liquor; mixing w1th the liquor a quantity of potassium and magnesium sulphates obtained in a later stage of the process; permitting crystallization of potassium sulphate from the resultant mixture and removing the same from the system; mixing with the resultant liquor a second quantity of potassium and magnesium sulphates obtained in a later stage of the process; aerating the resultant mixture to evaporate Water and to cause crystallization of mixed crystals of potassium and magnesium sulphates; separating the resultant mixture of potassium and magnesium sulphates and utilizing the same as the first -mentioned quantity of potassium and magnesium sulphates added to the liquor as above stated; heating the resultant liquorfand t 'from ores containing the same which comprises heating the ore sufficiently to expel Water of crystallization; leaching the orel While still hot With Water todissolve the potassium and magnesium sul hates; removing the undissolved gypsum rom the resultant liquor; mixing With the liquor a quantity of potassium and magnesium sulphates; permitting crystallization of potassium sulphate from the resultant mixture and removing the same from the system; mixing with the resultant liquor a second quantity of potassium and magnesium sulphates; and recovering magnesium sulphate from the mixture.

4. The process of recovering gypsum, potassium sulphate, and magnesium sulphate from ores containing the same which comprises heating the ore sufficiently to dehydratethe same; extracting the potassium and magnesium sulphates With hot Water; separating the undissolved gypsum from the resultant solution; crystallizing potassium sulphate out of the solution; separating the potassium sulphate crystals from the liquor; and treating the latter for recovery of magnesium sulphate.

5. The process of recovering gypsum, potassium sulphate, and magnesium sulphate from polyhalite which comprises heating the l sium and magnesium sulphates obtained in a later stage o the process; ermitting crystallization of potassium su phate from the resultant mixture and removing the same from the system; mixing with the resultant liquor apsecond quantity of potassium and magnesium sulphates obtained in a later stage -of the process; treating theresultant mixture to cause crystallization of mixed crystals of -potassium and magnesium sulphates; separating the resultant mixture of potassium and ma esium sulphates and utilizing the same as t e first mentioned quantity o-,potassium and magnesium sulphates added to the liquor as above stated; treating the resultant liquor to cause crystallization of a second mixture of potassium and magnesium sulphates; separating said second mixture and utilizing the same as the second mentioned quantitv of potassium and magnesium sulphates added to the liquor as above stated; and recovering magnesium sulphate from the remaining liquor.

6. The process of recovering gypsum, potassium sulphate, and magnesium sulphate from polyhalite which comprises heating the ore sufficiently to dehydrate the same; extracting the potassium and magnesium sulhates vhy treatment with hot Water; removlng the undissolved gypsum from the resultant liquor; mixing with the liquor a crop of mixed crystals of potassium and magnesium sulphates containing a greater proportion of potassium sulphate than magnesium sul phate; permitting crystallization of potassium sulphate from the resultant mixture and removing the same from the system; mixing with the resultant liquor a second crop of mixed crystals of potassium and magnesium sulphates containing a greater proportion of magnesium sulphate than potassium sulfrom ores containing the same; the steps which comprise extracting the potassium and magnesium sulphates from the ore by leaching with hot water; separating the resultant liquor from the undissolved gypsum; mixin with the liquor a quantity of potassium an magnesium sulphates; permitting crystalliza tion of potassium sulphate from the resultant mixture and removing the same from the s. stem; and treating the remaininr liquor or crystallization of magnesium sulphate.

In testimony whereof I ailix my signature.

' EUGENE P. SCHOCH.

phate; and recovering magnesium sulphate from the mixture.

7. The process of recovering gypsum, potassium sulphate, and magnesium sulphate from polyhalite and like ores which comprises dehydrating the ore; treating the dehydrated ore with hot Water to extract potassium and magnesium sulphates; separating the undissolved gypsum from the liquor; adding to the liquor crystals of potassium sulphate to accelerate crystallization in the liquor; permitting potassium sulphate to crystallize out of the liquor; removing the resultant potassium. sulphate crystals; and recovering magnesium sulphate from the remaining liquor.

8. In a method for recovering gypsum, potassium sulphate, and magnesium sulphate 

